1. Field of the Invention
This invention relates to circuit protection devices which comprise conductive polymer PTC elements.
2. Summary of the Prior Art
Conductive polymer PTC compositions are well known, and for details of recent developments relating to such compositions and devices comprising them, reference may be made for example to U.S. Pat. Nos. 4,017,715 (Whitney et al.), 4,177,376 (Horsma et al.) and U.S. Ser. Nos. 750,149 (Kamath et al.), 732,792 (Van Konynenburg et al.), 751,095 (Toy et al.), 798,154 (Horsma et al.), 873,676 (Horsma), 965,343 (Van Konynenburg et al.), 965,344 (middleman et al), 965,345 (Middleman et al.), 6,773 (Simon), 41,071 (Walker), and 97,711 (Middleman et al). It has been proposed to use devices comprising PTC elements to protect circuits against fault conditions arising from excessive temperatures and/or circuit currents--see for example U.S. Pat. Nos. 2,978,665 (Vernet et al.), 3,243,753 (Kohier) and 3,351,882 (Kohler), U.K. Pat. No. 1,534,715, the article entitled "investigations of Current Interruption by Metal-filled Epoxy Resin" by Littlewood and Briggs in J. Phys D: Appl. Phys. Vol. II. pages 1457-1462, and the article entitled "The PTC Resistor" by R. F. Blaha in Proceedings of the Electronic Components Conference, 1971, and the report entitled "Solid State Bistable Power Switch Study" by H. Shulman and John Bartho (August 1968) under Contract NAS-12-667, published by the National Aeronautics and Space Adminstration. However, it is only very recently, as described in U.S. Ser. Nos. 965,344 (Middleman et al.) and 6,773 (Simon), that circuit protection devices comprising conductive polymer PTC elements have become a practical reality.
The disclosure of each of the patents, patent applications and publications referred to above is incorporated by reference herein.